replace_object: don't check read_replace_refs twice

Since e1111cef (inline lookup_replace_object() calls,
May 15 2011) the read_replace_refs global variable is
checked twice, once in lookup_replace_object() and
once again in do_lookup_replace_object().

As do_lookup_replace_object() is called only from
lookup_replace_object(), we can remove the check in
do_lookup_replace_object().

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

replace_object.c

@@ -97,9 +97,6 @@ const unsigned char *do_lookup_replace_object(const unsigned char *sha1)
 	int pos, depth = MAXREPLACEDEPTH;
 	const unsigned char *cur = sha1;
 
-	if (!read_replace_refs)
-		return sha1;
-
 	prepare_replace_object();
 
 	/* Try to recursively replace the object */